Magneto ignition system for internal combustion engines

ABSTRACT

In a magneto ignition system where the magneto generator has two windings with a different number of turns, a diode is connected between the winding with the larger number of turns and the capacitor, the discharge of which through the spark coil generates the ignition voltage. The two windings are excited in phase. A second diode is connected between the two windings in such a way that when there is a positive voltage half-wave of the polarity which causes the first diode to conduct, the second diode is blocked so long as the winding with the larger number of turns has a voltage exceeding that across the winding with the smaller number of turns. At higher speeds the second diode conducts, thus preventing the capacitor voltage at ignition time from dropping with increasing speed. During voltage half-waves of the opposite polarity, when both windings are unloaded, the second diode conducts at whatever the speed the engine is running, reducing the peak voltage by the equalizing current that flows and thus protects the first diode against the possibility of excessive back voltage.

United States Patent [191 Chudoba 1 MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES [75] Inventor:

[73] Assignee: Robert Bosch G.m.b.ll., Stuttgart,

Germany 221 Filed: Nov. 8, 1913 21 Appl. No.: 413,975

Peter Chudoba, Nurnberg, Germany [30] Foreign Application Priority Data Nov. 11, 1972 Germany 2255396 [52] US. Cl...... 123/149 R; 123/148 E; 123/149 A; 123/149 D [51] Int. Cl. F02p 3/06 [58] Field of Search 123/148 E, 149 R, 149 A, 123/149 D [56] References Cited UNITED STATES PATENTS 3,461,851 8/1969 Stephens 123/148 E X 3,464,397 9/1969 Burson 123/148 E 3,630,185 12/1971 Struber et a1. 123/148 E 3,661,132 5/1972 Farr 123/148 E maxi/my [451 July 8,1975

Primary Examiner-Charles .l. Myhre Assistant Examiner-Tony Argenbright Attorney, Agent, or Firm-William R. Woodward ABSTRACT ln a magneto ignition system where the magneto generator has two windings with a different number of turns, a diode is connected between the winding with the larger number of turns and the capacitor, the discharge of which through the spark coil generates the ignition voltage. The two windings are excited in phase. A second diode is connected between the two windings in such a way that when there is a positive voltage half-wave of the polarity which causes the first diode to conduct, the second diode is blocked so long as the winding with the larger number of turns has a voltage exceeding that across the winding with the smaller number of turns. At higher speeds the second diode conducts, thus preventing the capacitor voltage at ignition time from dropping with increasing speed. During voltage half-waves of the opposite polarity, when both windings are unloaded, the second diode conducts at whatever the speed the engine is running, reducing the peak voltage by the equalizing current that flows and thus protects the first diode against the possibility of excessive back voltage.

5 Claims, 4 Drawing Figures MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES This invention relates to an ignition system for an internal combustion engine, of the magneto type in which a capacitor is charged by at least one diode and is discharged through a spark coil at the proper ignition time when a semiconductor switching element is put into its conducting condition. More particularly, the invention relates to ignition systems of that type in which the magneto generator has two armature windings in which an alternating current of the same phase is generated, with at least the armature winding with the larger number of turns being connected to the capacitor over a diode.

An important goal for all magneto ignition systems is the provision of reliable ignition over the entire speed range of the internal combustion engine, and for this purpose it is desired to provide an almost constant charge level of the capacitor over this speed range.

It is known to provide magneto ignition systems with two armature windings having a different number of turns, with each winding connected to the ignition capacitor over a diode. The armature winding with the larger number of turns induces a voltage that is suffcient for full charging of the capacitor in the lower speed range. In the upper speed range this voltage decreases with increasing speed, however, because the time for charging of the capacitor is reduced and the charging current is limited by the flux linkage dependent upon the pole wheel running around the armature and by the counterflux produced by the charging current. In the upper speed range, therefore, the second armature winding having a smaller number of turns, becomes effective, because the magnetic flux penetration and the counterflux is substantially smaller in this armature winding.

Such a solution has the disadvantage, however, that the negative half-waves produced in the armatures are blocked by the diodes and are therefore unloaded. A very high blocking voltage stress is therefore produced in the upper speed range, particularly for the diode connected to the armature winding with the larger number of turns. It is further known to protect the diodes during the negative voltage half-wave by providing a voltage dependent resistor (VDR) across each of the armature windings or by limiting the negative halfwaves by a supplementary short-circuit winding provided on the armature of the magneto generator.

These remedies have the disadvantage, however, that the positive half-waves, which are used for charging the capacitor, are likewise loaded, in an undesirable way, and that. furthermore, an appreciable amount of heat is developed at the places in the magneto generator where these elements are provided. In addition, such protection means are costly in materials and assembly.

It is an object of this invention to provide a magneto ignition system in which the negative voltage halfwaves produced in the armature windings are limited without additional damping means and without producing heating of the magneto generator.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the armature winding with the smaller number of turns is connected to the end of the armature winding with the larger number of turns over a second diode so connected that in the presence of a voltage half-wave producing conduction in the first diode connected between the armature winding with the larger number of turns and the capacitor) the second diode has voltage applied to it in the blocking direction, so long as the voltage produced by the winding with the larger number of turns is greater than that produced by the winding with the smaller number of turns.

The invention is further described by way of example with reference to the annexed drawing, in which:

FIG. 1 is a diagram of an ignition system for a one cylinder internal combustion engine;

FIG. 2 is a graph showing the capacitor voltage reached at the time of ignition as a function of the speed of the engine, and

FIGS. 3a and 3b show, for the lower speed range and the higher speed range respectively, the time course of voltage half-waves in the two armature windings operating in unloaded condition.

The ignition system shown in FIG. 1 comprises a magneto generator 10 having a field rotor (pole wheel) 11 driven by the internal combustion engine. The rotor 11 has permanent magnets of alternating polarity evenly distributed about its periphery surrounding a stator consisting of an armature plate 13 on which are provided on opposite sides two armatures l4 and 15. Each of these armatures is provided with an armature winding 16,17, these armature windings differing in wire cross-section and in the number of turns. The flux 1 linking the armature windings l6 and I7 for the position of the field rotor 11 shown in FIG. I is designated by an arrow for each of these windings. The two windings l6 and I7 are connected in phase, with their ends 16a and 17a connected to ground or chassis and with their other ends 161; and 17b connected together through a diode l8 and then connected over another diode 19 to a capacitor 20, which has its other connection likewise grounded. The primary winding 21a of a spark coil 21, in series with a semiconductor controlled rectifier (SCR) 22 are connected in parallel with the capacitor 20. The secondary winding 21b of the spark coil 21 has one end connected to the primary winding 21a and the SCR 22 and its other end connected by an ignition cable 23 with a spark plug 24 of the internal combustion engine.

The two armature cores l4 and 15 are mounted within the magnet bearing rim of the field rotor ll of the magneto generator 10. They are provided in the form of chord-type armatures mounted on opposite halves of the armature plate I3, so that in every position of the field rotor 11 they are linked by approximately the same magnetic flux b The armature winding 16, which has the smaller number of turns, about 1400 turns, has one end 16b connected to the anode of the diode 18, which is connected in series with the diode 19, the cathode of which is connected both with the primary winding 21a of the spark coil 21 and with the ungrounded connection of the capacitor 20. The armature winding 17 has about 8000 turns and has one end 17b connected to the interconnection of the diodes l8 and 19, where it connects with the cathode of the diode l8 and the anode of the diode 19.

The voltage diagrams given in FIG. 2, FIG. 3a and FIG. 3b serve to explain the manner of operation of this ignition system. FIG. 2 shows the dependence of the voltage at the capacitor 20 upon the speed n of the internal combustion engine. In the lower speed range a greater voltage U17 is induced in the winding 17 that has the larger number of turns than in the winding 16 with the smaller number of turns. The positive halfwaves of this alternating voltage are supplied to the capacitor 20 over the diode 19, charging the capacitor to a voltage U by the time of ignition, when the capacitor is discharged by the switching of the SCR into its conducting condition by a signal applied to its control electrode. The discharge of the capacitor through the primary winding 21a of the spark coil induces a high voltage pulse in the secondary winding 21b to produce a spark in the spark plug 24. The value of the voltage U is shown for various engine speeds by the solid line in FIG. 2.

Operation in the low speed range is also shown in FIG. 3a, which shows the time course of the voltage during positive and negative half-waves in unloaded condition of the armature windings 16 and 17 which, as mentioned before, are energized in phase. The voltage U17 in the winding 17 is considerably higher than the voltage U16 of the armature winding 16. Accordingly, for the positive voltage half-waves, the voltage U17 reaches the capacitor 20 over the diode 19, whereas the positive half-wave of the voltage U16 is blocked by the diode 18, because the higher voltage U17 is applied to its cathode. When the negative halfwave arrives, the diode 18 becomes conducting, because the voltage U16 at the anode of the diode 18 is less negative than the voltage U17. An equalization current accordingly flows through both armature windings 16 and 17 which limits the negative half-wave at the output of the magneto generator to the extent shown by the dashed curve in FIG. 3a. The diode 19 is thus protected against excessive back voltage in the low speed range by the voltage limiting effect just described.

ln the higher speed range of the engine the voltage U17 induced in the armature winding 17 falls off. On the other hand. the voltage U 16 induced in the winding 16 with the lower number of turns increases. The course of the voltage of the positive and negative halfwaves is shown in FIG. 3b. As soon as the voltage U16 in the winding 16 exceeds the voltage U17 in the winding 17, the former reaches the capacitor 20 over the diodes 18 and 19. As shown in FIG. 2, in this higher speed range the voltage U16 takes over the charging of the capacitor 20. On account of the voltage difference in the two windings l6 and 17, an equalization current now flows during the positive half-waves through the winding 17, so that the voltage at the output of the magneto generator 10 has the magnitude shown in the dashed line in FIG. 3b. The unloaded negative voltage half-waves, however, still produce a more negative voltage U17, which is applied to the cathode of the diode 18, than the voltage U16 which is applied to the anode of the diode 18, so that this diode is conducting, just as in the case at lower speeds. The diode 18, therefore, is protected also in this case, because the voltage difference (U 17 U16) drives a current through the armature windings 16 and 17 and through the diode 18 that limits the negative voltage half-waves at the output of the magneto generator 10 to the magnitude shown by the dashed curve in FIG. 3b.

Although the invention has been described with reference to a particular example, it is not limited thereto and variations and modifications are possible within the inventive concept. The diodes 18 and 19 can also perform their functions at other positions of the circuit. What is essential is that the diode 18 is so connected between the co-phased parallel connected armature winding 16 and 17 that in the presence of a voltage half-wave that causes the diode 19 to conduct, the diode 18 is blocked at speeds at which the winding 17 delivers a higher voltage under load than the winding 16.

In the case of magneto generators that are required to supply, in addition to an ignition system, other electrical devices, for example the lighting system of a motor cycle, it is appropriate, in order to obtain the cophased parallel connection of the two armature windings 16 and 17, to arrange the two armatures l4 and 15 in parallel in the magnetic circuit. That can be simply done by a superposed arrangement of the armatures in which one is placed over the other, as seen from the axial direction, so that their pole faces are simultaneously reached and passed by the revolving magnets 12 as they proceed around their circular path.

I claim:

1. A magneto ignition system for an internal combustion engine, comprising:

a capacitor;

a spark coil having its primary winding in circuit with a semiconductor switch and said capacitor and having its secondary winding in circuit with at least one spark plug of said engine;

means for closing said semiconductor switch at the desired ignition time for said engine to produce a spark;

said magneto generator having first and second arm ature windings positioned so as to be excited in phase synchronism, said first winding having a substantially larger number of turns than said second winding;

a first diode (19) connected between one end (16b) of said first winding (16) and said capacitor (20) for the charging of said capacitor by said generator; and

additional diode rectifying means (18) connected in series with said second armature winding (17), the series combination of said second armature winding (17) and said additional diode rectifying means (18) being connected in parallel with said first armature winding, said additional diode rectifying means being so poled that during a generated halfwave of polarity such that said first diode conducts, said second diode is blocked so long as the voltage across said first winding exceeds the voltage across said second winding.

2. A magneto ignition system as defined in claim 1 in which each of said armature windings is wound on a chord armature arranged within a multiple pole field rotor (11) and supported on opposite halves of an armature plate (13).

3. A magneto ignition system as defined in claim 1 in which the respective armatures (14,15) carrying the armature windings (16,17) are magnetically in parallel with each other.

4. A magneto ignition system as defined in claim 3 in which the two armatures (14,15) are in superimposed arrangement.

5. A magneto ignition system as defined in claim 1 in which said additional diode rectifying means (18) is a diode connected between one end (17b) of said second armature winding (17) and the common connection of one end (16b) of said first armature winding (16) and said first diode (19). 

1. A magneto ignition system for an internal combustion engine, comprising: a capacitor; a spark coil having its primary winding in circuit with a semiconductor switch and said capacitor and having its secondary winding in circuit with at least one spark plug of said engine; means for closing said semiconductor switch at the desired ignition time for said engine to produce a spark; said magneto generator having first and second armature windings positioned so as to be excited in phase synchronism, said first winding having a substantially larger number of turns than said second winding; a first diode (19) connected between one end (16b) of said first winding (16) and said capacitor (20) for the charging of said capacitor by said generator; and additional diode rectifying means (18) connected in series with said second armature winding (17), the series combination of said second armature winding (17) and said additional diode rectifying means (18) being connected in parallel with said first armature winding, said additional diode rectifying means being so poled that during a generated half-wave of polarity such that said first diode conducts, said second diode is blocked so long as the voltage across said first winding exceeds the voltage across said second winding.
 2. A magneto ignition system as defined in claim 1 in which each of said armature windings is wound on a chord armature arranged within a multiple pole field rotor (11) and supported on opposite halves of an armature plate (13).
 3. A magneto ignition system as defined in claim 1 in which the respective armatures (14,15) carrying the armature windings (16, 17) are magnetically in parallel with each other.
 4. A magneto ignition system as defined in claim 3 in which the two armatures (14,15) are in superimposed arrangement.
 5. A magneto ignition system as defined in claim 1 in which said additional diode rectifying means (18) is a diode connected between one end (17b) of said second armature winding (17) and the common connection of one end (16b) of said first armature winding (16) and said first diode (19). 